U.S. patent application number 13/876373 was filed with the patent office on 2013-08-29 for light emitting diode component comprising polysilazane bonding layer.
This patent application is currently assigned to 3M INNOVATIVE PROPERTIES COMPANY. The applicant listed for this patent is Guoping Mao, Terry L. Smith, Yu Yang, Stephen J. Znameroski. Invention is credited to Guoping Mao, Terry L. Smith, Yu Yang, Stephen J. Znameroski.
Application Number | 20130221393 13/876373 |
Document ID | / |
Family ID | 46084569 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130221393 |
Kind Code |
A1 |
Mao; Guoping ; et
al. |
August 29, 2013 |
LIGHT EMITTING DIODE COMPONENT COMPRISING POLYSILAZANE BONDING
LAYER
Abstract
In one embodiment, a semiconductor component, such as a
wavelength converter wafer, is described wherein the wavelength
converter is bonded to an adjacent inorganic component with a cured
bonding layer comprising polysilazane polymer. The wavelength
converter may be a multilayer semiconductor wavelength converter or
an inorganic matrix comprising embedded phosphor particles. In
another embodiment, the semiconductor component is a pump LED
component bonded to an adjacent component with a cured bonding
layer comprising polysilazane polymer. The adjacent component may
the described wavelength converter(s) or another component
comprised of inorganic material(s) such as a lens or a prism. Also
described are methods of making semiconductor components such as
wavelength converters and LED's.
Inventors: |
Mao; Guoping; (Woodbury,
MN) ; Znameroski; Stephen J.; (Eagan, MN) ;
Yang; Yu; (Eden Prairie, MN) ; Smith; Terry L.;
(Roseville, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mao; Guoping
Znameroski; Stephen J.
Yang; Yu
Smith; Terry L. |
Woodbury
Eagan
Eden Prairie
Roseville |
MN
MN
MN
MN |
US
US
US
US |
|
|
Assignee: |
3M INNOVATIVE PROPERTIES
COMPANY
ST. PAUL
MN
|
Family ID: |
46084569 |
Appl. No.: |
13/876373 |
Filed: |
October 25, 2011 |
PCT Filed: |
October 25, 2011 |
PCT NO: |
PCT/US11/57635 |
371 Date: |
March 27, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61415115 |
Nov 18, 2010 |
|
|
|
Current U.S.
Class: |
257/98 |
Current CPC
Class: |
H01L 33/0093 20200501;
H01L 33/44 20130101; H01L 2924/0002 20130101; H01L 2933/0025
20130101; H01L 2933/0041 20130101; H01L 33/502 20130101; H01L
2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/98 |
International
Class: |
H01L 33/50 20060101
H01L033/50 |
Claims
1. A semiconductor component comprising a wavelength converter
bonded to an adjacent inorganic component with a cured bonding
layer comprising a polysilazane polymer.
2. The semiconductor component of claim 1 wherein the wavelength
converter is a multilayer semiconductor wavelength converter or an
inorganic matrix comprising embedded phosphor particles.
3. The semiconductor component of claim 1 wherein the wavelength
converter is a multilayer semiconductor wavelength converter
comprising II-VI semiconductor material.
4. The semiconductor component of claim 1 wherein the multilayer
semiconductor wavelength converter absorbs a portion of blue light
to produce longer wavelengths.
5. The semiconductor component of claim 1 wherein the bonding layer
further comprises up to 10 wt-% of free-radically polymerizable
monomer.
6. The semiconductor component of claim 5 wherein the
free-radically polymerizable monomer is a (meth)acrylate
monomer.
7. The semiconductor component of claim 6 wherein the
(meth)acrylate monomer is a multi-(meth)acrylate monomer comprising
at least three (meth)acrylate groups.
8. The semiconductor component of claim 1 wherein the adjacent
component is a cover sheet.
9. A light emitting diode (LED), comprising: a pump LED component
bonded to an adjacent component with a cured bonding layer
comprising polysilazane polymer.
10. The light emitting diode (LED) of claim 9 wherein the LED
component and adjacent component are comprised of a material which
is stable at temperature greater than 150.degree. C.
11. The light emitting diode (LED) of claim 9 wherein the LED
component and adjacent component are comprised of one or more
inorganic materials.
12. The light emitting diode (LED) of claim 9 wherein the pump LED
comprises III-V semiconductor material.
13. The light emitting diode (LED) of claim 9 wherein the adjacent
component is a wavelength converter, lens, or prism.
14. The light emitting diode (LED) of claim 13 wherein the
wavelength converter is a multilayer semiconductor wavelength
converter or an inorganic matrix comprising embedded phosphor
particles.
15. The light emitting diode (LED) of claim 9 wherein the light
emitting diode (LED) further comprise a cover sheet.
16. The light-emitting diode (LED) of claim 13 where the wavelength
converter is bonded to the cover sheet with a cured bonding layer
comprising a polysilazane polymer.
17. An electronic illuminated display comprising: a
light-transmissive inorganic component bonded to an adjacent
inorganic component with a cured bonding layer comprising a
polysilazane polymer.
18. The electronic illuminated display of claim 17 wherein the
light-transmissive inorganic component is the light emitting diode
(LED) of claim 9.
19. A method of making a semiconductor component comprising:
bonding a wavelength converter wafer, pump LED component, or
combination thereof to an adjacent component with a bonding layer
comprising polysilazane polymer.
20. The method of claim 19 wherein a wavelength converter is bonded
to an inorganic light-transmissive cover sheet.
21-24. (canceled)
Description
BACKGROUND
[0001] Wavelength converted light emitting diodes (LEDs) are
becoming increasingly important for illumination applications where
there is a need for light of a color that is not normally generated
by an LED, or where a single LED may be used in the production of
light having a spectrum normally produced by a number of different
LEDs together. One example of such an application is in the
back-illumination of displays, such as liquid crystal display (LCD)
computer monitors and televisions. In such applications there is a
need for substantially white light to illuminate the LCD panel. One
approach to generating white light with a single LED is to first
generate blue light with the LED and then to convert some or all of
the light to a different color. For example, where a blue-emitting
LED is used as a source of white light, a portion of the blue light
may be converted using a wavelength converter to yellow light. The
resulting light, a combination of yellow and blue, appears white to
the viewer.
[0002] In some approaches, the wavelength converter is a layer of
semiconductor material that is placed in close proximity to the
LED, so that a large fraction of the light generated within the LED
passes into the converter. WO2009/048704 describes a light emitting
diode (LED) that includes a wavelength converter for converting the
wavelength of light emitted by the LED. A bonding layer attaches
the LED wafer to the wavelength converter. Another approach is
direct wafer bonding of the semiconductor wavelength converter to
the semiconductor material of the LED die.
SUMMARY OF THE INVENTION
[0003] One approach to manufacture wavelength converted LED's is to
produce a plurality of LED semiconductor layers for multiple
devices on a common substrate, that are subsequently separated into
individual devices by use, for example, of a wafer saw. The
wavelength converter may be bonded to a cover glass, prior to
bonding the wavelength converter to the LED semiconductor layers.
Typically silicone adhesives have been used for this purpose due to
its superior optical clarity and excellent thermal stability.
However, it has been found that such silicone adhesives do not cut
cleanly during dicing with the wafer saw. Accordingly, industry
would find advantage is alternative adhesives that address such
problem without compromising the desired optical properties.
[0004] In one embodiment, a semiconductor component, such as a
wavelength converter wafer, is described wherein the wavelength
converter is bonded to an adjacent inorganic component with a cured
bonding layer comprising polysilazane polymer. The wavelength
converter may be a multilayer semiconductor wavelength converter or
an inorganic matrix comprising embedded phosphor particles.
[0005] In another embodiment, the semiconductor component is a pump
LED component bonded to an adjacent component with a cured bonding
layer comprising polysilazane polymer. The adjacent component may
the described wavelength converter(s) or another component
comprised of inorganic material(s) such as a lens or a prism.
[0006] Also described are methods of making semiconductor
components such as wavelength converters and LED's.
[0007] In each of these embodiments, the bonding layer may comprise
polysilazane polymer alone or a mixture further comprising a
free-radically polymerizable monomer such as a (meth)acrylate
monomer. Compositions comprising a (meth)acrylate monomer can
advantageously be radiation cured to maintain the positioning of
the assembled components prior to completion of curing by thermal
curing. Provided that the bonding layer comprises a relatively low
concentration of free-radically polymerizable (e.g. (meth)acrylate)
monomer(s), the optical clarity and thermal stability properties of
the polysilazane material are not substantially compromised.
[0008] In view of such favored properties, bonding layers
comprising polysilazane polymer is surmised to be suitable for use
as an optical adhesive for other light-transmissive inorganic
component of electronic illuminated display devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0010] FIG. 1 schematically illustrates an embodiment of a
multilayer semiconductor wavelength converter wafer bonded to a
cover glass;
[0011] FIG. 2 schematically illustrates an embodiment of a
wavelength-converted light emitting diode (LED);
[0012] FIGS. 3A-3E schematically illustrate process steps in an
embodiment of a manufacturing process for a wavelength converted
LED;
[0013] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0014] The present invention is applicable to bonding
semi-conductor layers such as wavelength converters, light emitting
diodes (LEDs), and other light-transmissive inorganic
components.
[0015] As used herein "wavelength converter" refers to a component
that converts wavelengths of at least a portion of the light
emitted by the LED to a different, typically longer, wavelength.
The wavelength converter may be a multilayer semiconductor
wavelength converter or an inorganic matrix comprising embedded
phosphor-particles. WO 2006/097876 and WO2010/024981, both
incorporated herein by reference; describe illustrative wavelength
converters comprising a ceramic matrix comprising embedded phosphor
particles. Such wavelength converters may also be referred to as
luminescent ceramic matrix composites.
[0016] In favored embodiments, the wavelength converter converts
light at the blue or UV portion of the spectrum into longer
wavelengths of the visible or infrared spectrum, so the emitted
light may appear to be, for example, green, yellow, amber, orange,
or red, or, by combining multiple wavelengths, the light may appear
to be a mixed color such as cyan,magenta or white. For example, an
AlGaInN LED that produces blue light may be used with a wavelength
converter that absorbs a portion of the blue light to produce
longer wavelengths such as yellow light, with the result that the
combination of blue and yellow light appears to be white.
[0017] More particularly, in some embodiments, the bonding of a
multilayer semiconductor wavelength converter using a polysilazane
bonding layer is described. One suitable type of semiconductor
wavelength converter 108 (See FIG. 1) is described in U.S. patent
applications Ser. No. 11/009,217 incorporated herein by reference.
A multilayered wavelength converter typically employs multilayered
semiconductor structures (e.g. quantum well structures) comprising
II-VI semiconductor materials, for example various metal alloy
selenides such as CdMgZnSe. In such multilayered wavelength
converters, the quantum well structure 114 is engineered so that
the band gap in portions of the structure is selected so that at
least some of the pump light emitted by the LED (102 of FIG. 2) is
absorbed. The charge carriers generated by absorption of the pump
light move into other portions of the structure having a smaller
band gap, the quantum well layers, where the carriers recombine and
generate light at the longer wavelength. This description is not
intended to limit the types of semiconductor materials or the
multilayered structure of the wavelength converter.
[0018] An example of (e.g. multilayer semiconductor) wavelength
converter wafer bonded to a glass cover sheet with a cured
polysilazane bonding layer is depicted in FIG. 1. The component 10
includes a semiconductor wavelength converter 108 attached to an
inorganic light-transmissive (e.g. glass) cover sheet 145 with a
cured polysilazane bonding layer 140.
[0019] An example of a wavelength-converted LED device 100
according to a first embodiment of the invention is schematically
illustrated in FIG. 2. The device 200 includes an LED 102 that has
a stack of LED semiconductor layers 104 on an LED substrate 106.
The LED semiconductor layers 104 may include several different
types of layers including, but not limited to, p- and n-type
junction layers, light emitting layers (typically containing
quantum wells), buffer layers, and superstrate layers. LED
semiconductor layers 104 generally comprise III-V semiconductor
materials.
[0020] The LED semiconductor layers 104 are sometimes referred to
as epilayers due to the fact that they are typically grown using an
epitaxy process. The LED substrate 106 is generally thicker than
the LED semiconductor layers, and may be the substrate on which the
LED semiconductor layers 104 are grown or may be a substrate to
which the semiconductor layers 104 are attached after growth, as
will be explained further below.
[0021] The upper and lower surfaces 122 and 124 of the
semiconductor wavelength converter 108 may include different types
of coatings, such as light filtering layers, reflectors or mirrors,
for example as described in U.S. patent application Ser. No.
11/009,217. The coatings on either of the surfaces 122 and 124 may
include an anti-reflection coating.
[0022] In some embodiments, semiconductor wavelength converter 108
is attached to the upper surface 112 of the LED 102 via a bonding
layer 110. Thus, bonding layer 110 bonds the wavelength converter
108 to the LED 102. Provided that LED 102 can withstand thermal
curing at temperatures necessary to thermally cure a polysilazane
adhesive, bonding layer 110 may alternatively or in combination
with bonding layer 140, comprise a cured polysilazane bonding
layer.
[0023] The bonding layers, and in particular the bonding layer 140
between the wavelength converter and inorganic light-transmissive
cover sheet comprises a curable polysilazane composition. The
curable polysilazane composition functions as an optical
adhesive.
[0024] As used herein, "polysilazane" refers to compounds having at
least one of a linear, branched, or cyclic backbone comprising at
least one Si--N linkage; these compounds comprise at least one
ethylenically-unsaturated group or a SiH group. For simplicity, in
this application, "polysilazane" also includes "polysiloxazane" and
"polyureasilazane". "Polysiloxazane" refers to compounds having at
least one of a linear, branched, or cyclic backbone comprising both
Si--N and Si--O linkages. "Polyureasilazane" refers to compounds
having at least one linear, branched, or cyclic backbone comprising
at least one Si--N linkage and having at least one carbonyl group
bonded to each of two nitrogen atoms. Polysilazane polymers are
distinguished from polysiloxane polymers in that although the
backbone of a polysiloxane comprises Si--O linkages, polysiloxanes
lack Si--N linkages.
[0025] Polysilazane polymers are known such as described in U.S.
Pat. No. 7,297,374; incorporated herein by reference.
[0026] Useful polysilazanes, all of which can be random,
alternating, or block polymers, include those linear polysilazanes
generally represented by Formula I,
##STR00001##
wherein R.sup.1 and R.sup.2 are independently H, a linear,
branched, or cyclic aliphatic group having less than 9 carbon
atoms, a linear, branched, or cyclic heteroalkyl group having less
than 7 carbon atoms, a substituted or unsubstituted aryl group
having less than 13 carbon atoms, an ethylenically unsaturated
group, or where R.sup.1 and R.sup.2, taken together, may form a
ring having less that 8 carbon atoms; R.sup.3 and R.sup.5 are
independently H, a linear or branched alkyl group having less than
7 carbon atoms, or a linear or branched heteroalkyl group having
less than 7 carbon atoms; R.sup.4 is H or an ethylenically
unsaturated group; a and b represent mole fractions such that the
sum of a and b is 1, b is greater than zero, and preferably a is
greater than b. The number average molecular weight of the
polysilazanes of Formula I can range from about 160 g/mol to about
10,000 g/mol, preferably from about 300 g/mol to about 7,000 g/mol,
more preferably from about 500 g/mol to about 3,000 g/mol, and most
preferably from about 700 g/mol to about 2,000 g/mol.
[0027] Examples of useful cyclic polysilazanes include those
generally represented by Formula II,
##STR00002##
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, a, and b are
as described for the polysilazanes of Formula I. The number average
molecular weight of the cyclic polysilazanes of Formula II can
range from about 160 g/mol to about 3,000 g/mol, preferably from
about 300 g/mol to about 2000 g/mol, and more preferably from about
350 g/mol to about 1500 g/mol. Examples of other useful cyclic
polysilazanes include those that include both linear and cyclic
polysilazanes moieties.
[0028] Examples of useful branched polysilazanes also include those
generally represented by Formula I (linear polysilazanes with
branches) or Formula II (cyclic polysilazanes with branches) where
either or both of R.sup.1 and R.sup.2 in at least one or more of
the repeat units of the polysilazanes have the structure
represented by Formula III
##STR00003##
wherein R.sup.5 is as described for Formula I, R.sup.6 is H, a
linear, branched, or cyclic aliphatic group having less than 9
carbon atoms, a linear, branched, or cyclic heteroalkyl group
having less than 7 carbon atoms, a substituted or unsubstituted
aryl group having less than 13 carbon atoms, an ethylenically
unsaturated group, and c represents a mole fraction such that the
sum of a, b, and c is 1, b is greater than zero, preferably b is
greater than c, c is greater than zero, and preferably a is greater
than b. The number average molecular weight of the branched
polysilazanes can range from about 160 g/mol to about 3,000 g/mol,
preferably from about 300 g/mol to about 2000 g/mol, and more
preferably from about 350 g/mol to about 1500 g/mol. Examples of
other useful branched polysilazanes include those that include
multiple branches and those that include cyclic polysilazane
moieties. Polysilazanes that include Si--O units in addition to
Si--N units are called polysiloxazanes and are useful in the
present invention.
[0029] Useful linear polysiloxazanes include those generally
represented by Formula IV,
##STR00004##
wherein R.sup.1, R.sup.2, R.sup.7, and R.sup.8 are independently H,
a linear, branched, or cyclic aliphatic group having less than 9
carbon atoms, a linear, branched, or cyclic heteroalkyl group
having less than 7 carbon atoms, a substituted or unsubstituted
aryl group having less than 13 carbon atoms, an ethylenically
unsaturated group, or where R.sup.1 and R.sup.2, or R.sup.7 and
R.sup.8, each pair independently taken together, form a ring having
less that 8 carbon atoms; R.sup.3 and R.sup.5 are independently H,
a linear or branched alkyl group having less than 7 carbon atoms,
or a linear or branched heteroalkyl group having less than 7 carbon
atoms; R.sup.4 is H or an ethylenically unsaturated group; e, f,
and d represent mole fractions such that the sum of e, f, and d is
1, f and d are each greater than zero, and preferably e is greater
than both of f and d. The number average molecular weight of the
polysiloxazanes of Formula IV can range from about 160 g/mol to
about 10,000 g/mol, preferably from about 300 g/mol to about 7,000
g/mol, more preferably from about 500 g/mol to about 3,000 g/mol,
and most preferably from about 700 g/mol to about 2,000 g/mol.
[0030] Useful polysiloxazanes may be cyclic or branched. Useful
cyclic polysiloxazanes include polysiloxazanes that have cyclic
portions that include Si--O linkages and polysiloxazanes in which
the Si--O linkages are not in the cyclic portion. Useful branched
polysiloxazanes include polysiloxazanes that are branched at either
or both the Si--N or the Si--O linkages.
[0031] A particularly useful commercially available polysilazane,
KION HTT1880 (available from KiON Corp (a unit of Clariant),
Huntington Valley, Pa.), has the structure:
##STR00005##
wherein n is an integer of 1-20, and R.sup.10 can be H or a vinyl
group.
[0032] Polysilazanes that include carbonyl groups that are bonded
to each of two nitrogen atoms are called polyureasilazanes and are
useful in the present invention.
[0033] Useful linear polyureasilazanes include those generally
represented by Formula VI,
##STR00006##
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, and R.sup.5 are as
described for the polysilazanes of Formula I, R.sup.9 is H, a
linear, branched, or cyclic aliphatic group having less than 7
carbon atoms, g, h, and i represent mole fractions such that the
sum of g, h, and i is 1, both h and i are greater than zero, and
preferably g is greater than h. The number average molecular weight
of the polyureasilazanes of Formula VI can range from about 160
g/mol to about 10,000 g/mol, preferably from about 300 g/mol to
about 7,000 g/mol, more preferably from about 500 g/mol to about
3,000 g/mol, and most preferably from about 700 g/mol to about
2,000 g/mol.
[0034] Useful cyclic polyureasilazanes include those generally
represented by Formula VII,
##STR00007##
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, and R.sup.5 are as
described for the polysilazanes of Formula I and R.sup.9 and g, h,
and i are as described for the polyureasilazanes of Formula VI. The
number average molecular weight of the cyclic polyureasilazanes of
Formula VII can range from about 160 g/mol to about 3,000 g/mol,
preferably from about 300 g/mol to about 2000 g/mol, and more
preferably from about 350 g/mol to about 1500 g/mol. Examples of
other useful cyclic polyureasilazanes include those that include
both linear and cyclic polyureasilazanes moieties.
[0035] Examples of useful branched polyureasilazanes include those
generally represented by Formula VI (linear polyureasilazanes with
branches) or Formula VII (cyclic polyureasilazanes with branches)
where either or both of R.sup.1 and R.sup.2 in at least one of the
repeat units of the polyureasilazanes have the structure
represented by Formula III as described above.
[0036] The optical adhesive or bonding layer optionally, further
comprises at least one free-radically polymerizable monomer,
oligomers or polymers, such as a (meth)acrylate monomer. The
inclusion of a sufficient concentration of free-radically
polymerizable monomer is amenable to providing an adhesive
composition having dual curing mechanism, i.e. a combination of
free-radically polymerizable moieties and thermally curable
moieties. In the assembly of optical components, it is advantageous
to first partially cure, by free-radical polymerization assembled
components in order to maintain their assembled position for
completion of curing by thermal curing. However, for other
embodiments, the bonding layer may comprise polysilazane in the
absence other free-radically polymerizable components such as
(meth)acrylate monomers. Hence, the curable polysilazane bonding
compositions are thermally curable and optionally cured or hardened
using light.
[0037] Suitable (meth)acrylates are described, for example, by
Palazzotto et al. in U.S. Pat. No. 5,545,676 at column 1, line 65,
through column 2, line 26, the description of which is incorporated
herein by reference and include mono-, di-, and poly-acrylates and
methacrylates (for example, methyl acrylate, methyl methacrylate,
ethyl acrylate, isopropyl methacrylate, n-hexyl acrylate, stearyl
acrylate, allyl acrylate, glycerol diacrylate, glycerol
triacrylate, ethyleneglycol diacrylate, diethyleneglycol
diacrylate, triethyleneglycol dimethacrylate,1,3-propanediol
diacrylate, 1,3-propanediol dimethacrylate, trimethylolpropane
triacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol
diacrylate, pentaerythritol triacrylate, pentaerythritol
tetraacrylate, pentaerythritol tetramethacrylate, sorbitol
hexacrylate, bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,
bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,
trishydroxyethyl-isocyanurate trimethacrylate, the bis-acrylates
and bis-methacrylates of polyethylene glycols of molecular weight
about 200-500, copolymerizable mixtures of acrylated monomers such
as those of U.S. Pat. No. 4,652,274, and acrylated oligomers such
as those of U.S. Pat. No. 4, 642,126, the descriptions of which are
incorporated herein by reference. Suitable reactive polymers
include polymers with pendant (meth)acrylate groups, for example,
having from 1 to about 50 (meth)acrylate groups per polymer chain.
Mixtures of two or more monomers, oligomers, and/or reactive
acrylate polymers can be used if desired.
[0038] In favored embodiments, the (meth)acrylate monomer is a
multi-(meth)acrylate monomer having 2 or more (meth)acrylate
groups. The meth(acrylate)monomer preferably comprises 3, 4, 5 or
more (meth)acrylate groups such as acrylate group.
[0039] Various multi-functional (meth)acrylate monomers are
commercially available from Sartomer Company, Inc., Exton, Pa. such
as a trifunctional acrylate ester (SR9012), trimethylolpropane
triacrylate (SR351), pentaerythritol triacrylate (SR444),
trimethylolpropane triacrylate (SR351LV), and dipentaerythritol
pentaacrylate (SR399LV). For improved thermal stability, it is
generally preferred to utilize multi-(meth)acrylate monomers
lacking hydroxyl groups.
[0040] The inclusion of a small concentration of (meth)acrylate
monomer or oligomer can render the adhesive composition partially
curable by (e.g. ultraviolet) radiation curing as previously
described. The concentration of (meth)acrylate monomer in the
polysilazane optical adhesive or bonding layer is typically at
least 2 wt-% or 3 wt-% based on the total wt-% solids of the
adhesive composition or cured bonding layer. However, the inclusion
of such can also reduce the thermal stability in comparison to
polysilazane polymer alone. Hence, the concentration of
(meth)acrylate monomer or oligomer is typically no greater than 15
wt-% or 10 wt-%.
[0041] The adhesive composition typically comprises at least one
free-radical initiator to increase the rate of curing. Useful
free-radical thermal initiators include for example, azo, peroxide,
persulfate, redox initiators, and combinations thereof. Various
thermal initiators are commercially available such as peroxide
initiators commercially available from Arkema Inc, Philadephia, Pa.
under the trade designations "Luperox P" (t-butyl peroxybenzoate),
"Luperox 233M75" (ethyl 3,3-di-(t-butylperoxy)butyrate), "Luperox
533M75" (ethyl 3,3-di-(t-amylperoxy)butyrate), and "Luperox TAP"
(t-amyl peroxybenzoate). When the polysilazane bonding layer
comprises a multifunctional (meth)acrylate monomer at a sufficient
concentration such that the bonding layer can be partially cured by
photocuring (prior to thermal curing), the polysilazane bonding
layer typically further comprises a photoinitiator such as
commercially available from Ciba Geigy under the trade designations
"Darocur 1173", "Darocur "4265", "Irgacure 1800", Irgacure 369",
Irgacure 1700" and "Irgacure 907"; and commercially available from
BASF, Charlotte, N.C. under the trade designations "Lucirin TPO
(2,4,6-trimethylbenzoy diphenyl phosphine oxide) and "Lucirin
TPO-L" (ethyl-2,4,6-trimethylbenzoyl phenylphosphinate). The
initiators can be used alone or in various combinations, at a
concentration of about 0.1 to 10 weight percent.
[0042] Prior to using the polysilazane adhesive to bond
semiconductor layers or other inorganic light-transmissive
component, any volatiles present, such as NH.sub.3 in the adhesive
composition are removed since the presence thereof has been found
to contribute voids or haze in the bonding layer. Such volatiles
can be removed by various methods known in the art such as by
allowing the adhesive composition to sit overnight in an enclosed
glove box with a nitrogen atmosphere and/or by outgassing in a
(e.g. room temperature) vacuum oven.
[0043] The polysilazane bonding material may be delivered to the
surface of the a light-transmissive inorganic component such as a
wavelength converter 208 or wavelength converter comprising an
inorganic matrix comprising embedded phosphor particles,
semiconductor layers of an LED (i.e. pump LED componentn), a (e.g.
cover) glass, or to both, using any suitable method. Such methods
include, but are not limited to, spin coating, knife coating, vapor
coating, transfer coating, and other such methods such as are known
in the art. In some approaches the bonding material may be applied
using a syringe applicator.
[0044] Polysilazane materials are very sensitive to moisture and
the curing is very sensitive to O.sub.2 (radical curing).
Therefore, the adhesive is preferably stored in a dry box and the
adhesive is preferably applied in an inert environment as can be
achieved by use of a nitrogen blanket.
[0045] The polysilazane materials are thermally cured and
preferably partially cured by free-radical polymerization prior to
thermal curing. The thermal curing of the polysilazane optical
adhesive can be conducted at various temperatures. Curing
temperatures no greater than 200.degree. C., and preferably less
than 175.degree. C. or 150.degree. C., generally do not degrade the
II-IV semiconductor materials of the wavelength converter and
LED.
[0046] The cured polysilazane bonding layer is generally thermally
stable at for relatively long periods of time (e.g. 20,000 hours at
125.degree. C.). Such thermal stability is evident under strong
blue light illumination. The bond strength is sufficiently
maintained in combination with good optical clarity, i.e.
substantially no discoloration of the optical adhesive, such as
yellowing. In favored embodiments, the polysilazane optical bonding
layer exhibits adequate bond strength and good optical clarity
after aging for 1, 2, 3, 4, or 5 weeks at high temperatures of at
least 160.degree. C., or 170.degree. C., or 180.degree. C., or
185.degree. C.
[0047] Bonding layers 110 and 140 are substantially transparent
such that most of the light passes through the bonded
light-transmissive components, such as through the wavelength
converter 108 and cover sheet 145 and/or through the LED 102 to the
wavelength converter 108. For example greater than 90% of the light
(e.g. emitted by the LED 102) may be transmitted through the
bonding layer, as well as the light-transmissive inorganic
components bonded by such. Bonding layers 110 and 140 are
preferably colorless and have sufficient color stability such that
the bonding layers do not generate color (e.g. yellow) upon
aging.
[0048] To facilitate wafer dicing, bonding layers 110 and 140 are
preferably prepared from a high modulus material. Optical adhesives
comprising polysilazane polymer, as described herein,
advantageously has a substantially higher modulus than polysiloxane
adhesive compositions. Whereas polysiloxane adhesives typically
have a storage modulus of about 2-3 MPa, polysilazane adhesive
compositions typically have a storage modulus of at least about 1
gigapascal (GPa) or greater. Without intending to be bound by
theory, it is surmised that the increase in modulus is related to
clean cutting and the reduction of adhesive residue on the saw,
etc. during mechanical separation into individual components (i.e.
dies). In some embodiments, the cured polysilazane bonding layer,
further comprising a (e.g. multifunctional) (meth)acrylate monomer,
has a storage modulus of at least 2, 3 or 4 GigaPascals (GPa). In
other embodiments, the polysilazane bonding layer comprises solely
a polysilazane polymer, such as available from KION under the trade
designation "HTT1880", and has a storage modulus of at least 5 or 6
GPa.
[0049] It is generally desirable to use a bonding layer 110 and
optionally 140 that has a relatively high thermal conductance: the
light conversion in the wavelength converter is not 100% efficient,
and the resultant heat can raise the temperature of the converter,
which may lead to color shifts and a decrease in the optical
conversion efficiency. The thermal conductance can be increased by
reducing the thickness of the bonding layer 110 and by selecting a
bonding material that has a relatively high thermal conductivity. A
further consideration in selection of the bonding material is the
potential for mechanical stress created as a result of differential
thermal expansion between the LED, the wavelength converter, and
the bonding material. Two limits are contemplated. In the case
where the coefficient of thermal expansion (CTE) of the bonding
material is significantly different than the CTE of the LED 102
and/or wavelength converter 108, it is preferred that the bonding
material be compliant, i.e. have a relatively low modulus, so that
it can deform and absorb the stress associated with temperature
cycling of the LED. The adhesive properties of the bonding layer
110 are sufficient to bond the LED 102 to the wavelength converter
108 throughout the various processing steps used in manufacturing
the device, as is explained in greater detail below. In the case
where the CTE difference between the bonding material and the LED
102 semiconductor layers is small, higher modulus, stiffer bonding
materials may be used.
[0050] The bonding material 110 and optionally 140 may incorporate
inorganic nanoparticles to enhance the thermal conductivity, reduce
the coefficient of thermal expansion, or increase the average
refractive index of the bonding layer. Examples of suitable
inorganic particles include metal oxide particles such as
Al.sub.2O.sub.3, ZrO.sub.2, TiO.sub.2, ZnO, SnO.sub.2, and
SiO.sub.2. SiO.sub.2 nanoparticles are generally preferred. Other
suitable inorganic nanoparticles may include ceramics or wide
bandgap semiconductors such as Si.sub.3N.sub.4, diamond, ZnS, and
SiC. Suitable inorganic particles are typically submicron in size
so as to allow formation of a thin bonding layer, and are
substantially nonabsorbing over the spectral bandwidth of the
emission LED and the emission of the wavelength converter layer.
The size and density of the particles may be selected to achieve
desired levels of transmission and scattering. The inorganic
particles may be surface treated to promote their uniform
dispersion in the bonding material. Examples of such surface
treatment chemistries include silanes, siloxanes, carboxylic acids,
phosphonic acids, zirconates, titanates, and the like.
[0051] Generally, polysilazane optical adhesives and other suitable
materials for use in bonding layer 110 have a refractive index less
than about 1.7, whereas the refractive indices of the semiconductor
materials used in the LED and the wavelength converter are well
over 2, and may be even higher than 3. Despite such a large
difference between the refractive index of the bonding layer 110
and the semiconductor material on either side of the bonding layer
110, it has surprisingly been found that the structure illustrated
in FIG. 1 provides excellent coupling of light from the LED 102 to
the wavelength converter 108. Thus, the use of a bonding layer is
effective at attaching the semiconductor wavelength converter to
the LED without having a detrimental effect on extraction
efficiency, and so there is no need to use a more costly method of
attaching the wavelength converter to the LED, such as using direct
wafer bonding.
[0052] Coatings may be applied to either the light-transmissive
inorganic component, such as the cover sheet 145, wavelength
converter 108, or LED 102 or to improve adhesion to the
polysilazane bonding material and/or to act as antireflective
coatings for the light generated in the LED 102. These coatings may
include, for example, TiO.sub.2, Al.sub.2O.sub.2, SiO.sub.2,
Si.sub.3N.sub.4 and other inorganic or organic materials. The
coatings may be single layer or multi-layer coatings. surface
treatment methods may also be performed to improve adhesion, for
example, corona treatment, exposure to O.sub.2 plasma and exposure
to UV/ozone.
[0053] In some embodiments the LED semiconductor layers 104 are
attached to the substrate 106 via an optional bonding layer 116,
and electrodes 118 and 120 may be respectively provided on the
lower and upper surfaces of the LED 102. Bonding layer 116 is
typically a conductive metallic solder material. This type of
structure is commonly used where the LED is based on nitride
materials: the LED semiconductor layers 104 may be grown on a
substrate, for example sapphire or SiC, and then transferred to
another substrate 106, for example a silicon or metal substrate. In
other embodiments the LED employs the substrate 106, e.g. sapphire
or SiC, on which the semiconductor layers 104 are directly
grown.
[0054] In some embodiments, as depicted in FIG. 2 and described in
WO2009/048704; incorporated herein by reference, the upper surface
112 of the LED 102 is a textured layer that increases the
extraction of light from the LED as compared to the upper surface
112 being flat. The texture on the upper surface may be in any
suitable form that provides portions of the surface that are
non-parallel to the semiconductor layers 104. For example, the
texture may be in the form of holes, bumps, pits, cones, pyramids,
various other shapes and combinations of different shapes, for
example as are described in U.S. Pat. No. 6,657,236, incorporated
herein by reference. The texture may include random features or
non-random periodic features. Feature sizes are generally submicron
but may be as large as several microns. Periodicities or coherence
lengths may also range from submicron to micron scales. In some
cases, the textured surface may comprise a moth-eye surface such as
described by Kasugai et al. in Phys. Stat. Sol. Volume 3, page
2165, (2006) and US patent Publication No. US2006/0001056.
[0055] A surface may be textured using various techniques such as
etching (including wet chemical etching, dry etching processes such
as reactive ion etching or inductively coupled plasma etching,
electrochemical etching, or photoetching), photolithography and the
like. A textured surface may also be fabricated through the
semiconductor growth process, for example by rapid growth rates of
a non-lattice matched composition to promote islanding, etc.
Alternatively, the growth substrate itself can be textured prior to
initiating growth of the LED layers using any of the etching
processes described previously. Without a textured surface, light
is efficiently extracted from an LED only if its propagation
direction within the LED lies inside the angular distribution that
permits extraction. This angular distribution is limited, at least
in part, by total internal reflection of the light at the surface
of the LED's semiconductor layers. Since the refractive index of
the LED semiconductor material is relatively high, the angular
distribution for extraction becomes relatively narrow. The
provision of a textured surface allows for the redistribution of
propagation directions for light within the LED, so that a higher
fraction of the light may be extracted.
[0056] In other embodiments, methods of making wavelength
converters and wavelength-converted LEDs are described. The method
generally comprises bonding a semiconductor component, such as a
wavelength converter, pump LED semiconductor layers, or combination
thereof to an adjacent component with a bonding layer comprising
polysilazane polymer. For some embodiments, wherein the
semiconductor component is a wavelength converter, the adjacent
component is typically an inorganic light-transmissive (e.g. glass)
cover sheet 245 and/or pump LED semiconductor layers 204. The
adjacent component to the wavelength converter may also be another
optical element such as a converging extractor, as described in
U.S. Pat. No. 7,541,610; incorporated herein by reference. For
other embodiments, wherein the semiconductor component is a pump
LED, the adjacent component may be a wavelength converter, a lens,
a prism, or other optical element such as a converging extractor
(such as described in WO 2008/083188; incorporated herein by
reference). In either embodiment, the wavelength converted LED
comprises pump LED semiconductor layers adjacent to the
semiconductor wavelength converter opposing the cover sheet as
shown in FIGS. 2 and 3E.
[0057] Some exemplary process steps for constructing a
wavelength-converted LED device are now described with reference to
FIGS. 3A-3E. Pump LED wafer 200 is provided. A pump LED wafer
typically comprises LED semiconductor layers 204 over an LED
substrate 206, see FIG. 3A. In some embodiments, the LED
semiconductor layers 204 are grown directly on the substrate 206,
and in other embodiments, the LED semiconductor layers 204 are
attached to the substrate 206 via (e.g. metallic solder) bonding
layer 216. The upper surface of the LED layers 204 may be a
textured surface 212, as illustrated in FIGS. 3A-3E. The wafer 200
is provided with metallized portions 220 that may be used for
subsequent wire-bonding. The lower surface of the substrate 206 may
be provided with a metallized layer 218. The wafer 200 may be
etched to produce mesas 222. A layer of bonding material 210, is
disposed over the wafer 200. Such bonding material 210 may comprise
polysilazane or may comprise an alternative composition.
[0058] A multilayered semiconductor wavelength converter 208, grown
on a converter substrate 224, is attached to the polysilazane
bonding layer 210, as shown in FIG. 3B.
[0059] The wavelength converter 208 may be attached to the
polysilazane bonding layer using any suitable method. For example,
a measured quantity of bonding material, such as an adhesive, may
be applied to one of the wafers 200, 208 sitting on a room
temperature hot plate. The wavelength converter 208 or the LED
wafer 200 may be then attached to the bonding layer using any
suitable method. For example the flat surfaces of the wafers 200,
200 can then be roughly aligned one on top of the other and a
weight having a known mass can be added on top of the wafers 200,
208 to encourage the bonding material to flow to the edges of the
wafers. The temperature of the hot plate can then be ramped up and
maintained at a suitable temperature for curing the bonding
material. The hot plate can then be cooled and the weight removed
to provide the glue bonded converter-LED wafer assembly. In another
approach, a sheet of a selected tacky polymeric material can be
applied to a wafer using a transfer liner that has been die cut to
wafer shape. The wafer is then mated to another wafer and the
bonding material cured, for example on a hot plate as described
above. In another approach, a uniform layer of bonding material may
be pre-applied to the surface of the wavelength converter wafer and
the exposed surface of the bonding material protected with a
removable liner until such time as wafers 200 and 208 are ready to
be bonded. In the case of curable bonding materials, it may be
desirable to partially cure the bonding material so that it has
sufficiently high viscosity and/or mechanical stability for
handling while still maintaining its adhesive properties. The
partial cure may be accomplished using thermal curing. However, it
is preferred that the partial cure is accomplished by photocuring a
polysilazane bonding layer further comprising a multi(meth)acrylate
monomer.
[0060] The converter substrate 224 may then be etched away, to
produce the bonded wafer structure shown in FIG. 3C.
[0061] Once the extraction features have been etched, the
wavelength converter 208 is bonded to the inorganic
light-transmissive (e.g. glass) cover sheet 245 with a bonding
layer 240 comprising polysilazane polymer and optional
(meth)acrylate monomer, as depicted in FIG. 3D. After properly
positioning the inorganic light-transmissive (e.g. glass) cover
sheet with respect to the wavelength converter 208, the
polysilazane otpical adhesive is cured. In one embodiment, the
method comprises thermally curing the polysilazane bonding layer.
In another embodiment, the polysilazane composition comprises a
free-radically polymerizable (meth)acrylate monomer. The
polysilazane optical adhesive is first partially cured by radiation
curing to maintaining the positioning of the assembled components,
followed by heat curing to complete the curing of the polysilazane
polymer.
[0062] Vias 226 are then etched through the wavelength converter
208 and the bonding material 210 to expose the metallized portions
220, as shown in FIG. 3E.
[0063] For embodiments wherein a plurality of LEDs are fabricated
on a common substrate, the method, further comprises (e.g.
mechanically) separating the wavelength converted light emitting
diodes into individual wavelength converted LED dies. With
reference to FIG. 3E, the wafer may then be cut, for example using
a wafer saw, at the dashed lines 228 to produce separate wavelength
converted LED devices. Other methods may be used for separating
individual devices from a wafer, for example laser scribing and
water jet scribing. In addition to etching the vias, it may be
useful to etch along the cutting lines prior to using the wafer saw
or other separation method to reduce the stress on the wavelength
converter layer during the cutting step.
[0064] In view of the optical clarity and thermal stability
properties of the polysilazane optical adhesive described herein,
such polysilazane optical adhesive described herein are surmised
suitable for use as an optical adhesive for other optical
substrates, components, and devices. Since the polysilazane optical
adhesive described herein is thermally cured, the components or
substrates bonded with such optical adhesive typically have a glass
transition temperature substantially greater than the thermal
curing temperature. For example, the components, and/or assembly of
substrates bonded with such optical adhesive, are typically
thermally stable. In favored embodiments, the substrates have a Tg
of at least 150.degree. C., or 200.degree. C., or 250.degree. C.,
or greater. Hence, the optical adhesive is particularly useful for
bonding substrates and components that are comprised of one or more
inorganic materials, such as in the case of components of
electronic illuminated display devices.
EXAMPLES
[0065] Polysilazane polymer (PSZ) was obtained from KION
Corporation (a unit of Clariant), Huntington Valley, Pa.), under
trade designation HTT1880 with a possible structure shown as
follows:
##STR00008## [0066] SR351LV is a low viscosity trimethylolpropane
triacrylate (TMPTA, Mn: 296) obtained from Sartomer USA, LLC,
Exton, Pa. under trade designation SR351LV. [0067] SR444 is a
pentaerythritol triacrylate (solvent, 0.1%; water, 0.5%; Mn: 298)
obtained from Sartomer USA, LLC, Exton, Pa. under trade designation
SR444. [0068] SR295 is a pentaerythritol tetraacrylate; (water,
0.1%; solvent, 0.1%; acid, 0.05%, Mn: 352, m.p. 15-18 C) obtained
from Sartomer USA, LLC, Exton, Pa. under trade designation SR295.
[0069] SR399LV is a low viscosity dipentaerythritol pentaacrylate
(Mn: 525) obtained from Sartomer USA, LLC, Exton, Pa. under trade
designation SR399LV. [0070] SR9041 is a pentaacrylate ester
(solvent, 0.1%; water, 0.2%; acid, 0.1%) obtained from Sartomer
USA, LLC, Exton, Pa. under trade designation SR9041. [0071] DCP is
dicumyl peroxide obtained from Aldrich Chemical Company, Milwaukee,
Wis. was used as thermal initiator. [0072] DMAP is
2,2-dimethoxy-2-phenylacetophenone obtained from Aldrich Chemical
Company, Milwaukee, Wis. (also known as IRGACURE 651) was used as
UV initiator.
Example 1
[0073] Monochrome platelets consisting of II-VI converting layers
bonded to a glass wafer using polysilazane-acrylate blended
adhesives were fabricated. The starting substrate consisted of a
bottom substrate layer of InP with a GaInAs buffer layer followed
by the II-VI converting layers on top and were grown using
molecular beam epitaxial (MBE) process, similar to those described
in for example in WO2009/048704.
[0074] To promote adhesion of the II-VI material to the final LED
device, 300 nm of silicon nitride (Si.sub.3N.sub.4) and 100 nm of
SiO.sub.2 were deposited onto the II-VI layer at about 100.degree.
C. using plasma enhanced chemical vapor deposition (PECVD) method.
Prior to coating the Si.sub.3N.sub.4 and SiO.sub.2 layers, the
surfaces of the II-VI material were reactive ion etched (RIE) with
O.sub.2 plasma for 120 seconds then by argon plasma for 16
seconds.
[0075] The Si.sub.3N.sub.4/SiO.sub.2 coated side of the II-VI
material was bonded to a temporary glass carrier substrate to aid
in the removal of the InP substrate and GaInAs buffer layer. To
accomplish this, first, the II-VI/InP wafer was cleaved to the
desired size and then cleaned using acetone, methanol, and IPA
followed by drying using nitrogen gas. The glass carrier substrate
was cut to the appropriate size and cleaned using same procedure. A
wax powder (ROSS WAX 160, obtained from Frank B. Ross Co., Inc.,
Rahway, N.J.) was applied to the glass substrate and melted using a
hot plate at 205 C. The II-VI sample was placed on the wax and slid
around on the glass to remove bubbles. The II-VI/InP wafer and
glass were removed from the hotplate and allowed to cool.
[0076] Next, the InP substrate was removed in a two step process by
roughening and etching the InP layer. Roughening was performed by
placing the sample flat in a dish of water and sanding using 500
grit sandpaper until the entire surface had a matte finish. The
sample was then cleaned and dried. The InP was etched away by
immersing the sample in a 3:1 solution of HCl:H.sub.2O for 50-60
minutes. The sample was rinsed with de-ionized (DI) water and dried
using N.sub.2 gas.
[0077] After the InP was etched away, the InGaAs buffer layer were
removed in an acidic solution consisting of adipic acid, DI water,
ammonium hydroxide, and hydrogen peroxide. The etch time was about
10 minutes at which time the transparent specular II-VI layer was
revealed. The sample was rinsed thoroughly in DI water and
dried.
[0078] Extraction features to prevent light trapping in the II-VI
converting layers were formed on the top layer by patterning square
arrays of features having a pitch of 1 micron using a lithography
system. The patterns were etched in the II-VI material using
HBr:BR.sub.2 etchant at an etch time of more than 15 seconds. The
etch time was determined by the depth of etching desired. After
etching the patterns, the photoresist was removed and the
extraction features were coated with 60 nm Si.sub.3N.sub.4 using
PECVD technique.
[0079] The next step was to form platelets by bonding the II-VI
converted layers to a 0.5 mm thick glass cover. The adhesive
contained polysilazane (HTT 1800), 5 weight % multifunctional
acrylate (SR295) blend, and 1 weight % each of two initiators,
dicumyl peroxide (DCP) and 2,2 dimethoxy-2 phenol acetphenone
(DMAP). The PSZ-acrylate adhesive was prepared using the following
sequence: 1) 0.02 grams of the thermal and UV initiators were
weighed into a bottle; 2) 0.1 gram of SR295 was added and then 2
grams of PSZ; 3) the composition was placed in a glove box with a
nitrogen atmosphere overnight or placed in a 70.degree. C. oven for
10 min to dissolve the UV and thermal initiators; 4) the PSZ
solution was outgassed in a vacuum oven (at room temp) for 1.5
hours at 68 kPa vacuum; 5) the bottle containing the mixture was
removed from the vacuum oven and placed in a nitrogen atmosphere
with the lid open for 5 to 10 minutes; and 6) then the bottle was
closed while in the nitrogen environment.
[0080] Before bonding, the cover glass for the platelet was cleaned
on a spin coater at 3000 rpm using a sequence of sprayed acetone,
methanol, and isopropyl alcohol (IPA) while spinning The cover
glass was then dried by spinning for another 30 seconds after last
solvent rinse. The II-VI sample was cleaned with a quick rinse in
acetone, methanol, and IPA and dried in nitrogen.
[0081] To bond the II-VI converted layers to the glass cover, one
drop of PSZ adhesive was dispensed on a cleaned cover glass with a
pipette. The II-VI sample was placed II-VI side down onto the PSZ
drop, while applying pressure on the back of temporary carrier
glass with tweezers. Excess PSZ around the sample edges was cleaned
off with a swab. Curing of the adhesive was initiated by UV
exposure of the adhesive from the glass side. (The UV exposure for
B-staging the adhesive was accomplished using 5 cycles of 90 sec at
75 mW/cm.sup.2 in a flood exposure system, EFOS NOVACURE UV Light
Source). To thermally cure the PSZ, the sample was placed
platelet-glass side down onto a 120.degree. C. hot plate for 10
min. For the final cure, the hot plate temperature was increased to
170.degree. C. for 60 min.
[0082] The temporary carrier glass was slid to the side and removed
when the wax softened at 170.degree. C. on the hotplate. The sample
was allowed to cool and the temporary wax was removed using
acetone.
[0083] Before singulating the platelets, the top surface of the
II-VI was protected by placing the sample on a 100.degree. C.
hotplate and applying a low temperature wax. The sample was flipped
over onto a cleanroom wipe and the cover glass surface was cleaned
first with an acetone soaked swab and then with an isopropyl
alcohol soaked swab. An UV-release dicing tape (Nitto Denko
America, Inc., Santa Clara, Calif.) was applied to cover glass
surface to provide a carrier for the converter assembly during
dicing. The sample was then diced into individual platelets 1.0 mm
by 1.0 mm using a Disco model DAD522 dicing saw (Disco Hi-Tech
America, Inc., Santa, Clara, Calif.). After dicing, the protective
wax layer was removed with acetone, followed by a rinse of methanol
and isopropyl alcohol. The dicing tape released from the cover
glass after UV flood exposure for 30 sec @ 75 mW/cm.sup.2. The
diced edges of the adhesive were inspected and revealed no
stringing of the polysilazane adhesive.
Example 2
[0084] For Example 2 a PSZ (HTT 1800)--5 weight % acrylate adhesive
(SR9008) containing 1 weight % each of two initiators, dicumyl
peroxide (DCP) and 2,2 dimethoxy-2 phenol acetphenone (DMAP), was
prepared using the process described in Example 1.
Color Stability and % Transmission of Examples 1 and 2
[0085] For convenience, the following experiments were carried out
in air except the curing process.
[0086] Approximately 10 microliters of the adhesive of Example 1
and Example 2 were each dispensed on a separate previously cleaned
glass slides (2.5 cm.times.2.5 cm). The glass slides were cleaned
in an ultrasonic bath using DI water, acetone and methanol in
sequence. The slides and cover slips were then dried by blowing
nitrogen gas. A previously cleaned (as described above for glass
slides) glass cover slip (1 cm.times.1 cm) was placed on each glass
slide on the adhesive drop and the cover slip were pressed lightly
to spread the adhesives. Each slide-adhesive-cover slip was then
radiated for 5 minutes with UV light using an EFOS NOVACURE UV
Light Source. The intensity of light source at 365 nm was 20
mW/cm.sup.2. After the UV exposure (e.g., cure), the slides were
then placed in an oven set at 120.degree. C. for 15 minutes and
then the temperature of the oven was raised to 170.degree. C. The
adhesive was thermally cured at 1 hr at 170.degree. C. and the
samples were allowed to cool to room temperature for
evaluations.
[0087] The cured samples (cured in between glass slides) were aged
in an 185.degree. C. oven and monitored by UV-VIS spectroscopy.
After 3 weeks of aging at 185.degree. C., Example 1 was clear
indicating excellent thermal stability. Example 2 sample was clear
but had yellow edges.
[0088] The % transmission of Example 1 after 1, 2, and 3 weeks was
91-92% for wavelengths ranging from about 375 nm to 700 nm. The %
transmission of Example 2 after 1, 2, and 3 weeks was 91-92% for
wavelengths ranging from about 450 nm to 700 nm. The % transmission
at a wavelength of 400 nm was about 88%.
Examples 3-8
[0089] Various other adhesive comprising a mixture of PSZ (HTT
1800) and various acrylate monomers were prepared using the process
described in example 1. The acrylate monomer and concentration
thereof is described in the following table:
TABLE-US-00001 Example: Acrylate used: 3 10 wt-% SR295 4 5 wt-%
SR399LV 5 5 wt-% SR444 6 5 wt-% SR351LV 7 5 wt-% SR9041 8 5 wt-%
SR9012
[0090] The % transmission of Example 3 was evaluated in the same
manner as previously described. After 4 weeks of aging at
185.degree. C., Example 3 appeared to be thermally stable.
[0091] A study of the thermal stability of Examples 1 and 3 was
conducted using thermo-gravimetric analysis (TGA). The test results
indicated that such adhesives are thermally stable and usable up to
about 200.degree. C. or higher.
[0092] The % transmission of Example 3 after 5 weeks of aging at
185.degree. C. ranged from 90% to 93% for wavelengths of 400 nm to
700 nm
[0093] The % transmission of Examples 4-8 after 5 weeks of aging at
185.degree. C. was at least 89% for a wavelength of 400 nm and
91-93% for a wavelength of about 450 nm.
Example 9
[0094] For Example 9, a pure PSZ (HTT 1800) sample containing only
1 weight % of the thermal initiator, dicumyl peroxide (DCP) was
prepared using the process described in Example 1. Glass slides for
aging experiments were prepared using the PSZ adhesive as
previously described. The color stability and % transmission were
evaluated in the same manner as previously described. After 5 weeks
of aging at 185 C, Example 9 showed no visible color change and the
% transmission remained stable at 91-92% for wavelengths from 400
nm to 700 nm.
* * * * *